The present invention relates generally to an engine retarding device for an internal combustion engine and more particularly to a method and system for compression brake actuation.
Compression brakes or engine retarders are used to assist and supplement wheel brakes in slowing heavy vehicles, such as tractor-trailers. Compression brakes are desirable because they help alleviate wheel brake overheating. As vehicle design and technology have advanced, hauling capacity of tractor-trailers has increased, while at the same time rolling resistance and wind resistance have decreased. Thus, there is a need for advanced engine braking systems in heavy vehicles.
Known engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor. Typically, an exhaust valve located in a combustion cylinder opens when a piston in the cylinder nears a top dead center (TDC) position on a compression stroke.
In an effort to maximize braking power, some systems open the exhaust valve of each cylinder during a first opening event and a second opening event. In this manner, pressure released from a first cylinder into the exhaust manifold is used to boost the pressure of a second cylinder. Thereafter, the pressure in the second cylinder is further increased during the upstroke of the associated piston so that retarding forces are similarly increased. This mode of operation is termed xe2x80x9cback-fillingxe2x80x9d and is disclosed in U.S. Pat. No. 5,724,939 issued to Faletti et al on Mar. 10, 1998.
During the first opening event, the piston is at or near bottom dead center (BDC). During the second opening event, the piston is at or near TDC and pressures in the cylinder typically are higher than pressures in the cylinder during the first opening event. Forces required to move the exhaust valve during the second opening event are greater than those in the first opening event. Systems are typically designed to meet the higher opening forces required in the second opening event. Operating the exhaust valve with these higher opening forces may cause an exhaust valve actuating device to impact the exhaust valve or loose contact with exhaust valve when acting against the lower opening forces present in the first opening event. Loosing contact between the exhaust valve and valve actuating device or xe2x80x9covershootxe2x80x9d reduces controllability of the valve opening events. Further, impact between the exhaust valve and valve actuating device may cause premature wear of both the valve actuating device and the valve.
Additionally, pressures in the cylinder during compression will act to push the valve towards a valve seat when opening forces on the valve are removed. Oftentimes the valve may impact the valve seat to cause further damage to both the valve and valve seat. Damage due to interactions between the valve and valve seat result in reduced pressure ratios and decreased performance and efficiency in both power modes and braking modes.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a compression brake actuation device includes a brake actuator cylinder having a first port and a second port. A fluid conduit is in fluid communication with the first port and the second port. A brake actuator piston is positioned in the brake actuator cylinder. The brake actuator piston has a first actuating surface and a second actuating surface. The brake actuator piston has first piston passage through adapted to fluidly connect the first port with the first actuating surface. A second piston passage through the brake actuator piston fluidly connects the second port with the second actuating surface. The brake actuator piston is movable within the brake actuator cylinder to restrict fluid communication between the first port and the first piston passage. The brake actuator piston may also restrict fluid communication between the second port and the second piston passage.
In another aspect of the present invention, a method of actuating a compression brake system includes delivering a fluid to a first actuating surface. Delivery of the fluid is slowed by movement of a brake actuator piston.